Fair Value of Financial Instruments (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Balance Sheet Grouping, Financial Statement Captions
Carrying Value	$ 532.1	$ 534.6
Ark 2007 Subordinated Notes
Balance Sheet Grouping, Financial Statement Captions
Fair Value	0.0	30.5
Carrying Value	0.0	30.0
Ark 2021 Subordinated Notes
Balance Sheet Grouping, Financial Statement Captions
Fair Value	171.8	171.8
Carrying Value	155.4	155.5
HG Global Senior Notes
Balance Sheet Grouping, Financial Statement Captions
Fair Value	158.5	158.7
Carrying Value	147.0	146.9
Kudu Credit Facility
Balance Sheet Grouping, Financial Statement Captions
Fair Value	224.6	225.6
Carrying Value	203.8	203.8
Other Operations debt
Balance Sheet Grouping, Financial Statement Captions
Fair Value	27.4	30.0
Carrying Value	$ 25.9	$ 28.4